1. Field of the Invention
This invention relates to improvements in alloys having enhanced mechanical characteristics, and is particularly pertinent to substitutes of alloys, especially of the Cu/Zn type and the like. Furthermore, the subject invention relates to improved zinc-aluminum quaternary alloys and is particularly directed to methods of providing such alloys as stock material with excellent tensile strength.
2. Description of Prior Art
Zinc and various alloys thereof have generally been regarded as metals having mechanical properties that render them commercially unsuitable for wide structural usage. For an example, such metals normally have low tensile strength and poor resistance to deformation at relatively low stress levels even at ambient temperature. Formed articles when subjected to stresses at ambient temperatures, accordingly have not heretofore been made for structural application mainly due to these poor characteristics.
A number of compositions comprised of zinc alloyed with various elements are known by the prior art to have been fabricated to achieve certain end products. A general review of the relevant patents in this art is in order.
Winter, et al., U.S. Pat. No. 2,169,441 disclose that the working of an aluminum-bearing zinc base alloy containing from 10 to 20% aluminum at a temperature ranging from 518.degree. F., to 716.degree. F., improve the machinability, tensile strength and impact strength of said alloy. Generally, the relatively high copper content (Cu 1.5 to 4 percent) of this alloy and the disclosed thermal treatment do not permit production of a product with the high ultimate tensile strength that can be obtained by the method of the present invention.
Pelzel U.S. Pat. No. 2,982,677 discloses a method of manufacturing bearing alloys by heat treating Zn/Al/Cu alloys having at least 2.2% copper and less than 0.01%, preferable less than 0.005%, magnesium. Alloys produced by Pelzel have improved bearing properties but inferior mechanical properties to the present invention.
Hare, et al., U.S. Pat. No. 3,676,115 disclose an alloy comprising zinc within the range 70-82 weight percent, aluminum in the range of 18-30 weight percent, magnesium within the range from 0.05 to 0.25 weight percent and up to 2 weight percent of one or more of the elements copper, nickel and silver. The zinc alloys have exhibited ultimate tensile strengths of about 52,000 psi.
Chollet, et al., U.S. Pat. No. 3,741,819 relate to an alloy consisting essentially of 18-30% aluminum, up to 3% copper, up to 0.10% magnesium, up to 0.10% lithium and the balance zinc. The patent discloses a method of heat treating alloys to enhanced properties thereof by slow cooling the alloy from between about 380.degree. C., and about 290.degree. C. The alloy produced has a tensile strength of 43,600 psi.
Gervais, et al., U.S. Pat. No. 3,793,091 disclose ternary and quaternary zinc-aluminum alloys which are conditioned to exhibit superplastic behavior by hot working thereof at temperatures between about 205.degree. C. and the eutectoid temperatures of the alloy. In particular, the alloy of Gervais, et al., is produced by a rapid ice water quenching method followed by hot working.
Gervais, et al., U.S. Pat. No. 3,862,863 disclose a heat treatment for wrought zinc-aluminum alloys employing a two-stage cooling process. The first stage is the slow cooling of the alloy from above its eutectoid temperature, generally requiring an average rate of cooling less than about 3.0.degree. C., per minute followed immediately by a rapid-cooling step to ambient temperature.